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671.
A synthetic methodology for the synthesis of alpha-amino acid precursors directly from the corresponding aldehydes using N,O-dialkylated hydroxylamines and masked acyl cyanide (MAC) reagents was developed. The one-pot reaction can be carried out under mild conditions and without a separate purification step of the imino species. The method was applied to the synthesis of optically pure (+)-4-methylphenylglycine and the derivatives by using an Abiko-Masamune's tricyclic 1,2-oxazolidine as the chiral auxiliary. 相似文献
672.
Masahiko Hayashi Ken-ichi Okunaga Shunsuke Nishida Kenjiro Kawamura Kazuo Eda 《Tetrahedron letters》2010,51(51):6734-6736
Efficient oxidative transformation of thiols to disulfides took place in the presence of activated carbon under an oxygen (or air) atmosphere. The present oxidation method is available not only for a variety of thiols such as simple aromatic and aliphatic thiols but also for 3,4-dihydropyrimidin-2(1H)-thiones and N-Boc-l-cysteine. 相似文献
673.
R. H. Scheicher T. P. Das K. Ishida T. Matsuzaki S. N. Nakamura N. Kawamura K. Nagamine 《Hyperfine Interactions》2001,138(1-4):427-430
We are currently investigating the influence of vibrational effects on the strength of trapping of He+ in solid hydrogen. Such effects can lead to an isotope dependence of the trapping energy associated with the hydrogen molecules
and He+ ion. At the present time, our focus is on the isotope effect for 3He+ and 4He+, which we are studying through the vibrational motions of the trapped He+ ions in the potential they experience as they move about their equilibrium positions. The potential governing the vibrations
has been obtained from Hartree–Fock cluster calculations of the total energy of the cluster composed of the He+ ion and up to the third nearest neighbor hydrogen molecules as a function of the displacement of the He+ ion from its trapped position. The energy eigenvalues for the ground vibrational states of 3He+ and 4He+ in this potential come out as 1.29 and 0.96 meV, respectively, leading to corresponding reductions by these amounts in the
binding energy of 8.6 eV for both ions without vibrational effects. The difference of these reductions can be considered as
an isotope shift, its value for this case being 0.33 meV. From the analysis for these results, it is suggested that isotope
shift effects for deuteron and triton in solid D–T would have the same order of magnitude. A procedure for more accurate investigations
of the isotope shifts is discussed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
674.
The reaction of tris(2‐pyridyl)phosphine oxides with benzeneselenenyl chloride in methanol gave the corresponding 5‐phenylseleno‐2,2′‐bipyridyls together with a small amount of 2,2′‐bipyridyls. Similarly, the reaction with arenesulfenyl chlorides in aqueous acetonitrile afforded two kinds of coupling products, 5‐phenylthio‐2,2′‐bipyridyls and 2,2′‐bipyridyls. While in the reaction with arenesulfinyl chlorides in aqueous acetonitrile, four corresponding bipyridyl derivatives, 2,2′‐bipyridyls, 5‐arylthio‐2,2′‐bipyridyls, 5‐arylsulfinyl‐2,2′‐bipyridyls, and 5‐arylsulfonyl‐2,2′‐bipyridyls, were formed. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:72–81, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10085 相似文献
675.
Takuzo Aida Masakatsu Kuroki Hiroshi Sugimoto Tsuyoshi Watanabe Takato Adachi Chikara Kawamura Shohei Inoue 《Macromolecular Symposia》1993,67(1):125-135
Living anionic polymerization of methacrylic esters initiated with aluminum porphyrins ( 1 ) was found to be dramatically accelerated (e.g., 46 000 times) upon addition of bulky Lewis acids such as alkylaluminum diphenolates ( 3 ). Under appropriate conditions, a narrow MWD poly(methyl methacrylate) with Mn exceeding a million could be synthesized. The key conception of this high speed living polymerization is the coexistence of nucleophile ( 2 ) and Lewis acid ( 3 ) realized by steric repulsion. 相似文献
676.
Y Obora Y Ogawa Y Imai T Kawamura Y Tsuji 《Journal of the American Chemical Society》2001,123(43):10489-10493
Acylation of allylic esters (2) with acylsilanes (1) in the presence of a catalytic amount (5 mol %) of a palladium complex is reported. The reaction proceeds selectively to afford beta,gamma-unsaturated ketones (3) in high yields. [Pd(eta3-C6H5CH=CHCH2)(CF3COO)]2 (4a) showed the best catalytic activity. After the reaction, formation of CF3COOSiMe3 (5a) was confirmed by 29Si NMR measurement of the resulting reaction mixture, indicating the trimethylsilyl moiety effectively traps the CF3COO leaving group from 2. The leaving group of the allylic esters affects the reaction considerably: allylic trifluoroacetate gave the best result, while the corresponding acetates and trichloroacetates did not afford any acylation products at all. Stoichiometric reaction of 4a with 1 gave acylation product 3 with a formation of 5a and Pd(0), whereas no acylation reaction took place with the corresponding acetate complex [Pd(eta3-C6H5CH=CHCH2)(CH3COO)]2 (4b). A DFT calculation suggests that interaction of high-lying HOMO of 1 and low-lying LUMO of eta3-allylpalladium trifluoroacetate intermediate 4 would be indispensable in the catalytic cycle. 相似文献
677.
K. Akamatsu T. Kawamura S. Deki 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):305-308
Effect of composition on the dispersion of AuxCu1-x bimetallic nanoparticles into nylon 11 matrix has been investigated. TEM, EDX, and XPS depth profiling were used for characterizing
the changes in the composition of the bimetallic particles and in the depth distribution of the particles in the nylon 11
layer caused by heat treatment in N2 atmosphere. The island-like bimetallic particles were found to be formed on the nylon 11 surface before heat treatment. The
results of XPS depth profiling revealed that, by the heat treatment, the AuxCu1-x bimetallic particles with x? 0.55 were not dispersed into the nylon 11 layer while those with x≥ 0.70 were homogeneously dispersed in the films, indicating the existence of critical composition for penetration of the
bimetallic particles. By comparing the composition and structure of the bimetallic particles, the cause of these finding is
discussed in terms of surface free energy of the particles.
Received 29 November 2000 相似文献
678.
Vitor A. Fernandes Rafaely N. Lima Yoisel B. Broterson Meire Y. Kawamura Radell Echemendía Alexander F. de la Torre Marco A. B. Ferreira Daniel G. Rivera Marcio W. Paixo 《Chemical science》2021,12(48):15862
An efficient strategy combining the stereocontrol of organocatalysis with the diversity-generating character of multicomponent reactions is described to produce structurally unique, tetrasubstituted cyclopentenyl frameworks. An asymmetric Michael addition–hemiacetalization between α-cyanoketones and α,β-unsaturated aliphatic aldehydes was performed for constructing cyclic hemiacetals, which were next employed as chiral bifunctional substrates in a new diastereoselective intramolecular isocyanide-based multicomponent reaction. This approach furnished a diversity of structurally complex compounds – including peptidomimetics and natural product hybrids in high stereoselectivity (up to >99% ee and up to >99 : 1 dr) and in moderate to high yields.Simple and available reagents are combined in this new three-component isocyanide-based multicomponent reaction providing an interesting and straightforward way to prepare complex and highly functionalized cyclopentenyl rings. 相似文献
679.
680.